HFCs used for medical aerosols :
Asthma often occurs in the form of life-threatening, acute attacks which need immediate treatment. Therefore, patients always have to carry with them the necessary active substance in small pocket-sized dispensers, the metered dose inhalers. The dispenser contains a mixture consisting of the propellant and the pharmaceutical active substance dissolved or suspended in the liquified propellant and sometimes with further excipients such as co-solvents and/or surfactants added in very small amounts. This couple formulation dictates the choice between HFC-134a and HFC227ea, based on their different physico-chemical properties.
When the patient actuates the MDI, the propellant immediately evaporates at ambient conditions and produces a fine spray, the aerosol, which directly has to be inhaled via the mouthpiece.
Both HFC 134a and HFC 227ea were extensively tested by the International Pharmaceutical Aerosol Consortium for Toxicity Testing and were found to be toxicologically safe. Together with their chemical inertness and non-flammability they offer the degree of safety indispensable for this medical application.
In the MDI production process there is always a certain fraction of products that fail to meet the quality standards and are rejected during the quality control process. It is possible to remove the HFCs in these MDIs to recycle or safely destroy them in order to prevent their release into the atmosphere.
Measures to implement such recovery techniques at MDI manufacturing sites in the EU are currently in consideration respectively under development. Propellant recovery systems, once established, could also be applied for used MDIs which are still not completely empty.